Electrophysiologic effects of an acute beta-blockade induced by bisoprolol in patients with supraventricular tachycardia as assessed by His-bundle electrograms.

The acute electrophysiologic effects of 10 mg bisoprolol (B, given intravenously) were evaluated during an electrophysiological study in 10 patients with a history of paroxysmal tachycardia. Drug administration resulted in a significant decrease of sinus rate (Control [C]; 70.8/min; B: 59.4), and in an increase in sinus node recovery time (+20%). AV-nodal depression was marked at high heart rates during incremental atrial pacing. A second-degree AV-block occurred at a pacing cycle length (CL) of 329 ms (182/min) before and at a CL of 378 ms (158/min) after drug administration. Depression of AV-nodal conduction was negligible at low heart rates; the AH-interval at sinus rhythm was not affected (C: 84 ms, B: 86 ms); and functional and effective refractory periods of the AV-node were only slightly prolonged. Conduction intervals and refractory periods on atrial and ventricular level did not change. In 5 of 6 patients with accessory AV-pathways, circus movement tachycardia (CMT) could be elicited prior to as well as after B. Due to AV-nodal delay, CMT CL was slightly prolonged after B. Echozone and refractoriness of accessory pathways were not affected. In 1 of 2 patients with ectopic atrial tachycardia, B prevented the induction of paroxysms. In one patient with paroxysmal atrial fibrillation, the ventricular response decreased from 128/min to 94/min. The findings suggest that the electrophysiologic effects of B are due to a selective beta-adrenergic antagonism. Therapeutic efficacy is only to be expected if an increased adrenergic drive is a prerequisite for induction and continuation of a tachycardia.